Port "Show more"/"Show less" functionality from D7

+++ b/src/Plugin/facets/widget/LinksWidget.php
@@ -61,6 +62,12 @@ class LinksWidget implements WidgetInterface {
+    if (!empty($configuration['soft_limit'])) {
+      $build['#attached']['library'][] = 'facets/soft-limit';
+      $build['#attached']['drupalSettings']['facets']['softLimit'][$facet->id()] = (int) $configuration['soft_limit'];
+    }

Is this only empty when soft_limit is enabled?
No need to add the js library if its disabled I suppose

Okay, ignore my comment
I never use the empty command obviously ;)

Patch looks good.
I used data-attribute instead in the checkbox/dropdown widgets for passing on config to js, but we prolly should use drupal.settings as you did in this patch for more consistency. I'll create an issue for that.

Code is rtbc for me, but still needs manual testing.

patch from #8 was not working with me (both for lists and checkbox widget)
It looks like this is a js selector issue, as you already mentioned in #14

data-drupal-facet-id is on the parent div in my case, instead of the ul

Sure, doing right now.

Vanilla drupal with standard profile (so bartik) here.
Drupal 8.2.x

Great work, nice clean code!
Tested, works as expected.

Extremely minor nitpick, but this can also be fixxed while commiting I suppose.

RTBC for me

1. +++ b/src/Plugin/facets/widget/LinksWidget.php
   @@ -155,20 +162,30 @@ class LinksWidget implements WidgetInterface {
   +   * @todo This is inheriting noting. We need a method on the interface and,
   

   Extremely minor nitpick: Typo in todo ;) (not(h)ing)

2. +++ b/src/Plugin/facets/widget/LinksWidget.php
   @@ -155,20 +162,30 @@ class LinksWidget implements WidgetInterface {
   +    // @todo This should be handled upstream, in facet entity. Facet schema
   +    //   should be fixed and all configs should get sane defaults.
   

   Created an issue for this #2725453: Refactor widget plugins by adding interface, base class, schema

Dropdown got broken by this, fix coming up